💎 Resque::UniqueByArity

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resque-unique_by_arity composes queue-time and runtime uniqueness and lets each job choose which leading perform arguments define its uniqueness signature. It supports queue-local uniqueness, cross-queue uniqueness, and runtime uniqueness without hand-written Redis key methods.

Use it when a job has ancillary arguments, such as options or tracing values, that should not create a separate unit of work.

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Alternatively:

Install the gem and add to the application's Gemfile by executing:

bundle add resque-unique_by_arity

If bundler is not being used to manage dependencies, install the gem by executing:

gem install resque-unique_by_arity

Set application defaults with Resque::UniqueByArity.configure, then include a configured plugin instance in each job:

class RefreshAccount
  @queue = :accounts

  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_in_queue: true,
    unique_at_runtime: true,
    arity_validation: :error
  )
end

arity_for_uniqueness is the number of leading arguments used for the key. Use arity_for_uniqueness_at_runtime, arity_for_uniqueness_in_queue, or arity_for_uniqueness_across_queues when an enforcement axis needs a different arity. Choose either unique_in_queue or unique_across_queues, never both. arity_validation accepts :warning, :error, :skip, or nil/false.

The following is showing the default values. These global configs are copied into each per-class config unless they are overridden by the class config.

Create an initializer (e.g. config/initializers/resque-unique_by_arity.rb for rails) and customize the following:

Resque::UniqueByArity.configure do |config|
  config.logger = nil
    config.log_level = :debug
    config.arity_for_uniqueness = 0
    config.unique_at_runtime = false
    config.unique_in_queue = false
    # No need to do the following if keeping default values
    config.runtime_lock_timeout = 60 * 60 * 24 * 5
    config.runtime_requeue_interval = 1
    config.unique_at_runtime_key_base = "r-uar".freeze
    config.lock_after_execution_period = 0
    config.ttl = -1
    config.unique_in_queue_key_base = "r-uiq".freeze
    # Debug Mode is preferably set via an environment variable:
    #   to one of 'true', 'arity', or 'arity,queue,runtime' for all three tools:
    #     ENV['RESQUE_DEBUG'] = 'true'
    # config.debug_mode = true
end

This gem will take care to set the class instance variables (similar to the familiar @queue class instance variable) that are utilized by resque-unique_in_queue and resque-unique_at_runtime (default values shown):

# For resque-unique_at_runtime
@runtime_lock_timeout = 60 * 60 * 24 * 5
@runtime_requeue_interval = 1
@unique_at_runtime_key_base = 'r-uar'.freeze

# For resque-unique_in_queue
@lock_after_execution_period = 0
@ttl = -1
@unique_in_queue_key_base = 'r-uiq'.freeze

All you need to do is configure this gem accordingly:

  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    # Turn on one or both of the following:
    unique_at_runtime: false,
    unique_in_queue: false,
    # No need to do the following if keeping default values
    runtime_lock_timeout: 60 * 60 * 24 * 5,
    runtime_requeue_interval: 1,
    # would override the global setting, probably a bad idea.
    # unique_at_runtime_key_base: 'r-uar'.freeze,
    lock_after_execution_period: 0,
    ttl: -1,
    # would override the global setting, probably a bad idea.
    # unique_in_queue_key_base: 'r-uiq'.freeze
  )

Some jobs have parameters that you do not want to consider for determination of uniqueness. Resque jobs should use simple parameters, not named parameters, so you can just specify the number of parameters, counting from the left, you want to be considered for uniqueness.

class MyJob
  def self.perform(my, cat, is, the, best, opts = {})
    # Only the first 3: [my, cat, is] will be considered for determination of uniqueness
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 3,
    unique_at_runtime: true
  )
end

Want this gem to tell you when it is misconfigured? It can.

class MyJob
  def self.perform(my, cat, opts = {})
    # Because the third argument is optional the arity valdiation will not approve.
    # Arguments to be considered for uniqueness should be required arguments.
    # The warning log might look like:
    #
    #    MyJob.perform has the following required parameters: [:my, :cat], which is not enough to satisfy the configured arity_for_uniqueness of 3
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 3,
    arity_validation: :warning, # or :skip, :error, or an error class to be raised, e.g. RuntimeError
    unique_at_runtime: true
  )
end

Give the job a break after it finishes running, and don't allow another of the same, with matching args @ configured arity, to start within X seconds.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    lock_after_execution_period: 60,
    unique_at_runtime: true
  )
end

If runtime lock keys get stale, they will expire on their own after some period. You can set the expiration period on a per class basis.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    runtime_lock_timeout: 60 * 60 * 24 * 5, # 5 days
    unique_at_runtime: true
  )
end

Prevent your app from running a job that is already running.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_at_runtime: true
  )
end

Preventing jobs with matching signatures from running, and they never get dequeued because there is no actual corresponding job to dequeue.

How to deal?

MyJob.purge_unique_at_runtime_redis_keys

Prevent your app from queueing a job that is already queued in the same queue.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_in_queue: true
  )
end

Prevent your app from queueing a job that is already queued in any queue.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_across_queues: true
  )
end

Preventing jobs with matching signatures from being queued, and they never get dequeued because there is no actual corresponding job to dequeue.

How to deal?

Option: Rampage

# Delete *all* queued jobs in the queue, and
#   delete *all* uniqueness keys for the queue.
Redis.remove_queue('queue_name')

Option: Butterfly

# Delete *no* queued jobs at all, and
#   delete *all* uniqueness keys for the queue (might then allow duplicates).
Resque::UniqueInQueue::Queue.cleanup('queue_name')

Prevent your app from running a job that is already running, and prevent your app from queueing a job that is already queued in the same queue.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_at_runtime: true,
    runtime_lock_timeout: 60 * 60 * 24 * 5, # 5 days
    unique_in_queue: true
  )
end

Prevent your app from running a job that is already running, and prevent your app from queueing a job that is already queued in any queue.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    arity_for_uniqueness: 1,
    unique_at_runtime: true,
    runtime_lock_timeout: 60 * 60 * 24 * 5, # 5 days
    unique_across_queues: true
  )
end

Run your worker with RESQUE_DEBUG=true to see payloads printed before they are used to determine uniqueness, as well as a lot of other debugging output.

Redefine methods to customize all the things. Warning: This might be crazy-making.

class MyJob
  def self.perform(arg1)
    # do stuff
  end
  include Resque::Plugins::UniqueByArity.new(
    #...
  )

  # Core hashing algorithm for a job used for *all 3 types* of uniqueness
  # @return [Array<String, arguments>], where the string is the unique digest, and arguments are the specific args that were used to calculate the digest
  def self.redis_unique_hash(payload, arity_for_uniqueness = 1)
    #       for how the built-in version works
    # uniqueness_args = payload["args"] # over simplified & ignoring arity
    # args = { class: job, args: uniqueness_args }
    # return [Digest::MD5.hexdigest(Resque.encode(args)), uniqueness_args]
  end

  def self.unique_in_queue_redis_key_prefix
    # "unique_job:#{self}" # <= default value
  end

  def self.unique_in_queue_redis_key(queue, payload)
    # arity_for_uniqueness = determine_arity # over simplified & ignoring context-specific arity determination
    # unique_hash, _args_for_uniqueness = redis_unique_hash(payload, arity_for_uniqueness)
    # "#{unique_in_queue_key_namespace(queue)}:#{unique_in_queue_redis_key_prefix}:#{unique_hash}"
  end

  def self.unique_in_queue_key_namespace(queue = nil)
    # definition depends on which type of uniqueness is chosen, be careful if you customize
    # "r-uiq:queue:#{queue}:job" # <= is for unique within queue at queue time
    # "r-uiq:across_queues:job" # <= is for unique across all queues at queue time
  end

  def self.runtime_key_namespace
    # "unique_at_runtime:#{self}"
  end

  def self.unique_at_runtime_redis_key(*args)
    # payload = {"class" => self.to_s, "args" => args}
    # unique_hash, _args_for_uniqueness = redis_unique_hash(payload, configuration.arity_for_uniqueness_at_runtime)
    # key = "#{runtime_key_namespace}:#{unique_hash}" # <= simplified default
  end
end

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spec.add_dependency("resque-unique_by_arity", "~> 3.0")

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